1. Field of the Invention
The invention relates to a multi-lumen tube arrangement for use in a centrifuge free of a sliding seal and to a method for its manufacture, with the tube arrangement being rotated in the opposite direction towards its ends starting from a support position.
2. Description of the Related Art
Centrifuges free of sliding seals are known from the prior art, for example from DE 32 42 541 or DE 42 20 232. In this connection, a substance is broken down into its component parts and transported into separate containers via tubes. Since the containers are stationary, while the separation unit rotates, different solutions are known as to how the tube connection between the two should be guided. If one would like to dispense with a sliding seal in order to avoid contamination, the use of the above-mentioned centrifuges presents itself.
As represented in DE 26 12 988, the multi-lumen tube can consist of a single tube with a plurality of liquid channels, whereas DE 36 32 241 shows a tube arrangement of a plurality of individual tubes. In a centrifuge free of a sliding seal, the tubes or the multi-lumen tube arrangement are guided from a stationary connection point in a loop around the separation unit to the opposite side of the separation unit.
During operation of the centrifuge free of a sliding seal, the tube arrangement is connected to a drive unit which rotates at half the angular velocity or speed of the separation unit; furthermore, the tube arrangement rotates around itself. As a consequence of the different speeds between the drive unit and the separation unit, the tube arrangement untwines.
In this connection, the tube side lying radially further outside comes onto the inside and vice versa so that the whole tube arrangement is fulled. The outwardly disposed tube side is stretched while the inwardly disposed side is compressed, since the paths from the stationary connection up to the separation unit have a different length. For this reason, it is proposed in DE 36 32 241, to which reference is expressly made here, to wind individual tubes or tube lumens n+xc2xd times around the longitudinal axis of the tube or its parallel axes to make the path distances equal on average.
Furthermore, the tube arrangement is subject to high mechanical strain due to the centrifugal forces and this strain grows as the speed increases. The line forms an outwardly overhanging loop which is exposed to high flexural forces and/or abrasion forces at its ends. For this reason, the tubes are frequently supported in centrifuges free of sliding seals such as described in DE 198 03 534. These bearings can be roller bearings as in WO 95/17261 or plain bearings as in EP 0 112 990.
In a tube arrangement of a centrifuge free of sliding seals, a torque arises at the support position due to the bearing friction which has to be transmitted to the support position from both hose ends. This torque produces an additional strain on the tube in that it counters the torsion resistance of the tube and thus the service life.
It is the object of the present invention to further develop a tube arrangement of the kind first mentioned such that service life is further clearly increased while still allowing a cost-favourable manufacture. This object is solved by a multi-lumen tube arrangement for use in a centrifuge free of a sliding seal having at least two tubes of of aporoximately equal length, the individual tubes being rotated free of tension around their longitudinal axes and/or their parallel axes and being fixed at their ends. The tube arrangement has a support position and the individual tubes are wound around one another in opposite directions from the support position, with the tubes being fixed at their ends and to the support position. A method of manufacturing such a tube arrangement is also shown.
The tube arrangement in accordance with the invention consists of at least two individual tubes, which are rotated about one another about their longitudinal axes or their parallel axes and are fixed at their ends, and which has a support position from where the tubes are rotated around one another in the opposite direction up to their ends.
As a result of the desired untwining of the tube arrangement, the torque transmitted from the separation unit to the bearing is counter to that from the stationary position to the bearing. It has been found that the stability or service life of the tube arrangement suffers when the transmitted torque acts in the opposite direction to the tube rotation. Trials were therefore carried out which measure the service life of the tube arrangement in dependence on the rotational direction of the two tube ends starting from the bearing. The trials document a substantially increased stability when the torque acting on the tube arrangement extends in the same direction as the rotation of the individual hoses around one another, in each case starting from the support position to their two fixed ends. Since, as described above, the torques act opposite to one another, the rotation of the tubes around their longitudinal axes and/or around their parallel axes, continuing from the support position, is likewise in the opposite direction in accordance with the invention.
The tube arrangement can, as described in the prior art, consist of one tube with a plurality of lumens, which are then likewise wound around their longitudinal axes, or of a plurality of individual tubes. For reasons of simplicity, a multi-lumen tube arrangement having at least two individual tubes is spoken of here, where, however, a multi-lumen tube having more than two lumen is to be subsumed, with the individual lumen then extending in accordance with the invention in an opposite spiral shape starting from the support position.
The tubes used in accordance with the invention consist of a polymer material of one or more layers such as polyamide, polyurethane or PVC as well as in particular polyolefins such as polyethylenes or polypropylenes and their blends, with different materials being able to be used in different layers.
If the tubes are used in the medical sector, bio-compatible materials are naturally more suitable. Whereas, in the past, PVC tubes were common, polyolefin tubes have come into use in the meantime, preferably multi-layer polyolefin tubes whose hardness in each layer can be set by blends, also with ethylene styrenes.
The tube arrangement in accordance with the invention has a high strength with respect to elongation, kinking or turning by a suitable choice of the polymer materials and of the layers usedxe2x80x94whether in the form of extruded tubes or of laminated tubes. The inner diameter can also be kept constant substantially over the overall length so that there is no risk of clogging.
Such a tube arrangement usually consists of two to five lumens or single tubes, preferably four. The individual tubes are turned around the longitudinal axis of the tube arrangement or around a parallel axis hereto at least in partial regions so that a bundle twisted into itself is created. In this connection the twisting takes place according to conventional methods of stranding or braiding.
In this connection, the tube arrangement is fixed to the support position by clamping or bonding, for example, whereas the ends are disposed at holding pieces whose receiving bores still allow the movement of the individual tubes, that is are a little larger than the tube diameter so that an untwisting can take place. The individual tubes are thereby not under additional tension, which likewise reduces the service life of the tubes. In this connection, the turning preferably takes place n+xc2xd times, with n being zero or an integer. The individual tubes are particularly preferably turned 1.5 times.
In this connection, the individual tubes are fixed at the support position and the holding pieces, in which the individual tubes are first loosely held, are displaced towards the support position, rotated and pushed back into their starting position. The ends are then fixed in place, either by clamping into the holding piece or bonding in the holding piece or bonding the individual tubes.
In this connection, the manufacturing method is not limited to the procedure described above, but can naturally also take place in that the ends are already fixed in place, while the support position is pressed toward the holding piece, is turned and displaced back into its starting position again. In this connection, the bearing must have bores which are so large that they allow a separate movement of the tubes and avoid the twisting of the individual tubes around one another. Since, due to the turning of the support position, only one movement has to take place, with which simultaneously both tube parts are rotated in opposite directions, this simpler manufacturing method is preferred.